When human diploid fibroblasts (WI-38 cells) in culture are maintained under conditions non-permissive for growth (serum restriction), cell proliferation ceases, but the cells remain viable for extended periods of time. Under similar restrictive conditions non-permissive for growth, SV-40 transformed WI-38 fibroblasts (2RA cells) die off at a rate of 10 per cent per day. In resting WI-38 cells, the template activity of isolated nuclei is related to both cell density and the length of time the cells have been quiescent. In 2RA cells, nuclear template activity is related to time after plating, regardless of cell density. The results are compatible with the hypothesis that normal cells can enter a Go state more easily than transformed cells. This, in turn, would allow normal cells to survive under conditions non-permissive for growth, while transformed cells gradually die off.